Prior art components exist including two Hall effect probes or cells each constituted by a bar made of silicon, gallium arsenide, or indium antimonide, for example, into which an electrical current is injected. The bars are subjected to a magnetic induction field generally created by a permanent magnet such that a so-called "Hall" electrical voltage appears across the terminals of each bar.
This type of sensor constituted by associating a magnet with such a component serves to detect variation in the magnetic induction as appears, in particular, whenever an item having field-disturbing members moves past the probes. The moving item may be constituted, for example, by a toothed wheel. Such a sensor therefore serves to monitor positions and displacements and numerous applications are found therefor, in particular in the motor industry where such a sensor may be used, for example, to perform ignition functions or in antilock braking.
Development in integrated circuit technology has made it possible to provide components in the form of an integrated circuit having two probes that are a few millimeters apart, together with electronic processing stages associated with the probes. As can be seen in FIG. 1, Hall effect probes 1, 2 are connected to a differential amplifier 3 whose output is applied to a hysteresis comparator 4 such as a Schmitt trigger, as is well known per se. The probes 1, 2, the amplifier 3, and the comparator 4 are powered by an electrical voltage which is regulated by appropriate means 5.
The comparator 4 delivers a signal V via an output stage 6, which signal is representative of the difference in the induction detected by the probes 2 and 1 respectively, i.e. B=B.sub.2 -B.sub.1. As can clearly be seen in FIG. 2, the output signal V takes up a determined logic state, e.g. high, whenever the induction difference B between the two probes 1 and 2 is greater than the value of a high switchover threshold B.sub.H. The comparator 4 delivers an output signal having the complementary logic state (low in the example shown) whenever the induction difference B is less than a low switchover threshold B.sub.B. The operation of such a sensor thus presents a hysteresis cycle making it possible to obtain unambiguous transitions in the output voltage V for normal values of the induction (B.sub.H and B.sub.B) depending on whether it is increasing or decreasing, respectively.
Such components suffer from a major drawback in that they have relatively high manufacturing dispersion with respect to how the hysteresis cycle is determined, i.e. the switchover thresholds B.sub.H and B.sub.B. As can be seen clearly in FIG. 2, the value of the high switchover threshold B.sub.H may lie between values B.sub.Hmax and B.sub.Hmin, while the value of the low switchover threshold B.sub.B may lie in the range B.sub.Bmax to B.sub.Bmin.
Component manufacturing dispersion means that the outputs of different manufactured sensors do not take up a determined and reproducible logic state in the presence and in the absence of disturbing members to be detected. Such components cannot therefore be used directly in mass production of sensors including a magnet assembled to the component by means of glue, for example, without there being an increase in the cost of such a sensor due to specific operations that need to be performed in the assembly of each sensor.
In addition, another drawback of sensors of this type lies in the fact that their operation depends on the induction which appears at the surface of the magnet associated with each sensor being uniform, and in practice this is difficult to obtain.
The present invention therefore seeks to solve the above-mentioned drawbacks by providing a differential detection Hall effect component designed to compensate for the manufacturing dispersion that appears on the switchover thresholds which determine the hysteresis cycle in the operation of the level comparator associated with such a component.
The invention also seeks to provide a differential detection Hall effect sensor suitable for presenting magnetic induction at the surface of the magnet which is uniform or quasi-uniform.
The invention also seeks to provide a differential detection Hall effect sensor designed to retain the detection properties of large air gap sensors.